Virtually all types of drill rigs whether drilling for water, oil and gas, minerals or civil works and construction use drill rods and components that couple together to form a “drill string”. The drill hole is normally progressed by applying a rotation and a downward force to the drill bit at the bottom of the drill string. The drill string typically consists of drill rods, drill bits, stabilisers, “subs” and many other components which are normally all of a tubular form and connect with male and female threads. The threads are usually an integral part of each component and are required to withstand all the tensile, compressive and torque forces that are applied to the drill string by the drill rig. As the drill hole progresses more components are added to the drill string until the final borehole depth is achieved.
To give strength to the coupling or “joint”, and to avoid loosening while drilling, the joints in the drill string are often “made up” to a predetermined torque, and sometimes may become even tighter because of drilling conditions. When the drill string needs to be retrieved from the hole, the drill rods and components are removed by gradually withdrawing the drill string from the hole until (usually) one component at a time is exposed. The component below the one to be removed is held securely, allowing the upper component to be unscrewed and removed from the drill area. This cycle continues until all components are retrieved from the hole.
Unscrewing components of the drill string is often called “breaking out” the components. This is normally achieved with reverse rotation of the drill rig “rotation head” or “rotation gearbox”. If the drill string has been over-tightened or if the drill rig head is not capable of breaking the joint, then extra assistance to break the joint is required. When this occurs a “breakout tool” is used to break or loosen the joint. The breakout tool usually consists of a holding “tong” which grips the drill string component, and a means of rotating the tong about the drill string centre. Currently in the industry various types of tong are used to grip the components including wrap-around chain type, pipe wrench type and other clamping designs. Many types of tongs are self-tightening, so that once they gain a minimal grip on the component they will progressively grip tighter as torque is applied. These prior art tools are generally attached to a hydraulic cylinder pulling tangentially to the drill string axis to essentially give a rotating force to the tong and subsequently the drill string component.
In the mineral exploration and water well drilling industry, breakout tools are used regularly. Existing breakout units have often been made from modified pipe wrenches attached to hydraulic cylinders, and there are many such ad hoc arrangements in use. The components in the drill string vary in diameter so the breakout tools need to be capable of gripping a range of diameters. Prior art breakout tools are usually manually adjusted to the component size, or parts of them exchanged to change the gripping size. The breakout tools are also manually applied to the drill string by a worker and often have to be supported by hand until load is applied and they begin to grip the component.
There are considerable forces involved in the breaking process, often up to several tonnes of pull required from the hydraulic cylinder. As many breakout tools are adapted from tools not designed or rated to handle these forces, failures do occur. The act of manually adjusting and applying most types of prior art breakout tools exposes workers to severe hazards as they work in close proximity to the breakout tool. There are many injuries associated with the use of traditional type breakout tools.
The present invention was developed with a view to providing a breakout tool that can be readily adjusted and applied to drill string components without exposing workers to unacceptable safety hazards.
References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.